Gear Pumps & Motors Failure Analysis Guide

1 1. The heart of a hydraulic hydraulic system is the hydraulic pump. pump. The pump is the component that converts mechanical energy into fluid energy. A healthy pump pump will allow the hydraulic system on mobile equipment to ’ v v . Without a healthy pump, the system will be less responsive and rob the machine of performance and productivity. productivity. A properly maintained maintained hydraulic system provides insurance that the equipment will deliver the work it is designed to do. A good preventative maintenance maintenance program affords the operator hundreds of hours of trouble free operation.

FAILURE FA I LU RE ANALYSIS/ A N A LYS YSII S/ TROUBLESHOOTING GEA R PUM PS & M O TORS

Unfortunately, the hydraulic system does not always perform at its’ its’ specified level. It is at these times that we need to troubleshoot the system and pinpoint the cause. A proper diagnosis is critical to providing renewed performance and extended life. This booklet is designed to help you properly properly identify the . Commercial Intertech’s gear pumps and motors.

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© 1998 Commercial Intertech Corp.

Commercial Intertech is a worldwide manufacturer of fixed displacement hydraulic gear pumps and motors. With facilities on four continents Commercial is positioned to provide product and service to the global market place. For the past 75 years Commercial Intertech has been the product of choice for meeting the needs of tough mobile applications. . e eart eart o t e y rau rau c syst ystem, em, ommerc erc a nter nterte tecc ’ s exte extern rnaa spu spurr gear ear pum pumps are a fixed displacement design. For every complete revolution of of the gear shaft the pump displaces a fixed amount of oil. Pump output flow is proportional proportional to the engine speed. There are three casting components that make make up the exterior pump capsule: shaft end, gear housing, and port end cover. A tandem pump will have a fourth casting component, the bearing carrier. Various casting materials are used including including gray iron (the most common), compacted graphite, ductile iron, and aluminum. ear and dr ve sha ts are cut rom a oy stee stee and then then case case hard hardene ened. d. he most most commo common n gear shaft is the integral, where the drive shaft shaft and gear are one piece. The integral gear shaft provides exceptional exceptional torque carrying capabilities. The other type is the “continental” “continental” shaft and drive gear or the two piece. The “continental” shaft is machined machined with drive extensions on both ends of the shaft; an external drive (splined or keyed) and a smaller splined end end for internal drive. The drive Thrust

GEAR PUMP Plates End Cover

Mounting Flange

Port End

Lip Seal

inserting the small end of the shaft into the hub of an internally splined drive gear. Roller Bearings

Drive Spline Drive Gear Idler Gear Inlet Port Out Board Bearing

No matter what type of gear shaft used, the gear journals must be supported by bearings or sleeve type bushings. bushings. The roller bearing bearing pumps require the use of ring seals to prevent the hi hi h pressure pressure oil oil that that lubricate lubricatess the bearings from traveling down the shaft. Bushing pumps do not need ring seals as the bushings are lubricated with low pressure oil. To insure maximum pumping efficiency

2 3. Tandem pumps pumps are needed when there are multiple functions, functions that require different flows and where a single section can v . tandem pump shows the fourth casting component, the bearing carrier.

4. Both pumps pumps and motors employ a pressure . hydraulically balances the thrust plates and squeezes them against the two gear faces. The squeeze provides a seal between the gear face and the thrust plate surface preventing high pressure oil from slipping back to the low pressure side side of of the pump. Mechanical seals are used behind the thrust plate to block oil from slipping between the plate and adjoining casting.

TANDEM GEAR PUMP Bearing carrier

Pumping Sections 3


GEAR PUMP CUTAWAY

In the roller bearing units these seals are called pocket seals and are shown in the illustration. The sleeve bearing (bushing) units use a different kind of seal called a channel seal.

5. A cross sectional sectional view of the the pumping pumping chambers illustrates the flow path of the hydraulic oil through through the gear pump. pump. As the gears counter rotate the separating gear teeth create a vacuum drawing oil into the inlet. inlet. Oil is picked up by each tooth and carried around the outside of the gear, oil is not not drawn through the the center. The pockets between between the gear teeth and the housing are referred to as pumping chambers. As the gear gear teeth mesh on on the outlet side, oil is forced out of the pockets and exits the pump. ownstream res stance to the output ow causes an increase in pressure. High pressure pressure on the outlet side of the housing forces the gears to deflect into the low pressure (inlet) side. The tips of the gear teeth teeth contact the housing preventing high pressure output oil from leaking back to the low pressure inlet. Althou h necessar this tooth to housin contact can generate cast iron contaminant, contaminant, particularly in new units. Therefore, Commercial Intertech 100% tests all units before shipping, bringing them up to their

Bushings

OUT

IN Pressure Balanced

Thrust Plates

4


THRUST PLATE VIEW

OUTPUT

Force

Force

OIL FLOW

3 6. Contamination is the single single largest contributor to hydraulic component failures. Contamination is considered to be any

CONTAMINATION

6


MICRON

INCH

Grain of salt

100

.0039

Human hair

70

.0027

Lower limit of visibilty White blood cell

40

.00158

25

.001

Talcum powder

10

.00039

Red blood cell

8

.0003

Bacteria

2

.000078

7

8. Particle counting is the most common common method for determining cleanliness levels of hydraulic fluids. fluids. Powerful optical instruments are used to count the number of particles in a specified volume volume of fluid. fluid. There are several common cleanliness level standards, of these, the International Standards Organization code has gained wide acceptance.


ISO CODES ISO CODE

PARTICLES/ MILLILITER Fluid cleanliness > 5 micrometers > 15 micrometers required for

18/15

2,500

320

17/14

1,300

160

16/13

640

80

15/12

320

40

14/11

160

20

7. Particulate contamination contamination is measured across its largest diameter to determine size. This chart shows some comparative sizes of particles in microns (or micrometers). Commercial suggests the use of a 25 micron return line filter in systems with a pressure rating of 2500 psi (172 bar) or less. In systems rated between 2500 (172 bar) and 3000 psi recommended. A 10 micron return line filter is suggested for use with our P300 sleeve bushing pumps.

PARTICLE SIZES SUBSTANCE

specified by the oil producer. Water, dirt, dust, air, etc.... System cleanliness and regular preventative maintenance insure a long lasting, responsive hydraulic system.

Flow control valves, cylinders Gear pumps and motors Directional and pressure control valves Vane and piston pumps/motors Servo control valves

he code cons sts o two two ndex numbers numbers referring to the number of particles greater than 5 micrometers and 15 micrometers found in one milliliter of fluid. Maximum recommended contamination levels are a function function of component clearances and system operating operating pressure. As the system system pressure increases the oil film separating the working parts become thinner making the components more susceptible to damage by contaminant. Microscopic particles particles streaming streaming through the hydraulic components at high velocities pound the wear surfaces weakening and eroding material. Some particles particles get new components and remove metallic material from the the wear surfaces. This wear generates additional contaminant contaminant in the system and leads to leaks and a loss of component performance.

4 9. Read slide slide text.

CONTAMINATION • Improper filtration • Low oil level - concentration of contaminant • Loose or lost breather cap • Leaking fittings, seals, wi ers • Missing or collapsed inlet strainer • Poor fill practices • Clogged filter - by-pass

• Accelerated wear bearings, thrust plates, – bearings, housing

• Bearing / bushing failure • Reduced pump e c en e ncy • Reduced life • Heat • Internal leaks • Failed pump

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10. Nuts, bolts, screws, washers, plastic closures, shop rags, pieces of hose, etc.... can cause considerable damage to hydraulic pumps and other hydraulic hydraulic components. components. Many times the failures caused by large foreign objects occurs instantaneously as the pump ingests the debris and catastrophic failure results.


FOREIGN OBJECT ( N U TS & BO LTS) TS)

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11. The damage that occurred occurred to this gear set was caused by a hardened foreign object such as a screw or nut. nut. Additional debris has been been generated by the broken gear teeth and component scoring. This type of failure can contaminate the entire hydraulic system.


FOREIGN OBJECT DAMAGE

5

LARGE PARTICLE CONTAMINATION Motion

Gear

12. Particles too large to fit between the tight tight component tolerances will cause surface to surface contact removing material from the . surface, which provides a sealing surface between the high and low pressure oil leads to leaks and a loss of performance. Contamination Contamination in a hydraulic system is self perpetuating. As damage to internal components continues additional debris is generated by the wearing of the components.

Large particle contaminant

Thrust plate 12


SCORED THRUST PLATE

13. The pump thrust thrust plate is one one of the best places to look for evidence contributing to the pump failure. failure. The thrust plate plate is sometimes sometimes referred to as a wear plate. The score marks marks on the above plate were caused by particles being dragged across the plate surface by the hardened gear face.

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SCORED THRUST PLATE

14. New components provide provide a smooth, smooth, even surface allowing a continuous oil film to exist between the thrust thrust plate and gear face. When these surfaces become scored the oil film dissipates into the grooves interrupting the film. Metal to metal contact occurs, resulting in an increase in friction and heat. The grooved plate surface can also provide an escape route for high pressure oil to go back to low pressure inlet, resulting in a loss of .

6 15. P300 series plate shows score marks from large particle contaminant.

16. Microscopic particles particles the size of of airborne dust can accumulate in the tiny tolerances of today's hydraulic components. components. The accumulation can form a wedge between moving parts, increasing friction and accelerating wear. The velocity velocity of the tiny particles striking the wear surfaces can erode material weakening the wear surface and causing spalling. spalling. This erosion of metal leads

SCORED THRUST PLATE

15

FINE PARTICLE CONTAMINATION

adds additional contamination to the hydraulic system. All this adds up to a reduction reduction of system efficiency causing the engine to work harder, increasing fuel consumption. consumption. Roller bearings are more susceptible to fine particle contaminant than the bushing (sleeve type). type). The bushin bushin units, units, howev however, er, are more more susceptible to large contaminant than roller bearings.

17. As the gear teeth mesh mesh and oil is forced out of the pump outlet, a small amount of the oil is trapped by the meshing teeth in the tooth space root area (circled). The trapped oil is forced at right angles into the faces of the thrust plates. Relieved areas on the plates called trapping grooves allow the high pressure oil to escape. The high velocity velocity of the oil moving at a right angle to the thrust plate will do serious damage to the thrust plate v contamination is being carried by the oil.


Fine particle contaminants

r us p a e 16


THRUST PLATE VIEW

OUTPUT

Force

Force

OIL FLOW

7 18. The fine particles particles being carried by the hydraulic fluid erodes the thrust plate surface in the trapping groove on the high pressure . heaviest where the teeth mesh and then migrate towards the low pressure side of the plate. Over time, the wear cuts a channel into the plates’ surface allowing the oil to leak back to the pump inlet. The volumetric efficiency of the pump is reduced.

FINE PARTICLE CONTAMINATION

18


SCORED THRUST PLATE

19. A closer inspection of the plate surface not only reveals the damage in the center of the plate but in in the root seal seal area as well. A light ring around the I.D. root seal area develops due to the very tight tight clearances. Fine particles wear the thrust plate surface leaving a polished .

19


SCORED THRUST PLATE

20. This P300 thrust thrust plate shows shows evidence of fine particle contamination on the back side of the thrust late. Fine erratic tracks are cut into the plate surface around the balancing holes and low pressure area.

8 21. This thrust plate face shows erosion damage in the areas of high oil velocity, such as the trapping groove and balance holes.

SCORED THRUST PLATE

just below below the balance hole. The metal removed from the wear surfaces adds to the contaminated condition.

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22. Internal leakage is the primary cause cause of a loss of performance in a hydraulic system. Of the three factors identified above, control of critical clearances have the most dramatic impact. Wear, accelerated by contamination, contamination, heat, or pressure, will act to increase these critical clearances with disastrous results.


Leakage in Hydraulic Components +

2

Control of clearance critical

3

Q =flow (leakage)

1 0

23. When contamination contamination is present two wear wear bands will develop under the ring seals on the gear shaft of the the roller bearing pumps. These bronze high pressure seals are designed to reduce the high pressure oil lubricating the bearings to low pressure before reaching the shaft seal. Tiny particles, particles, under high pressure and velocity, progressively wear the gear journal surface until the ring seal is no longer effective. High pressure pressure jets under the the ring seal pressurizing the shaft seal area. The oil pressure on the shaft seal can force the seal lip away from the journal or even dislodge the seal from the bore. In both instances instances an external leak would would occur. Pump shaft seals are typically rated for a maximum pressure pressure of 15 to 20 psi. Shaft seals are sensitive sensitive to shaft speed, an increase in speed can cause a

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• eng o ea •Clearance •Pressure

2 3 © 1998 Commercial Intertech Corp.

WORN DRIVESHAFT

9

DRIVE SHAFT RING SEAL

24. When a seal leak is discovered discovered the first inclination for the maintenance maintenance staff can be to replace the shaft seal. This will not solve the roblem roblem.. The ear set and rin seals seals ma also also have to be replaced. A rule of thumb thumb for determining excessive excessive wear on the shaft is that if you can feel the wear with your finger nail it should be replaced. Ring seals are not needed in the bushing pumps as the bushings are lubricated with low pressure inlet oil.

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25. Contamination has caused wear bands to develop on this roller bearing motor gear. Closest to the spline end, the shaft has been grooved by dirt dirt trapped under the the lip seal. As the damage progresses external shaft seal leaks will develop. develop. Replacing the shaft seal seal at this point will not correct the leak as the undercut will prevent the proper squeeze of the seal on the shaft.

MOTOR SHAFT

Note: The contamination attacking the shaft seal area could also been brought in from the outside environment.

25


CAVITATION CAVITA AVITAT TI O N &

26. Excessive noise in in a hydraulic system system can be caused by the presence of air in the hydraulic oil. Air can be introduced into into the system two ways; through cavitation cavitation or aeration. “Cavitation” occurs occurs when the the pump inlet flow can no longer fill the pump chambers created by the separation of the gear teeth. The partial vacuum vacuum vaporizes some some of the oil causing air and or water to come out of solution. av a on s t e ormat on o a r, an water or oil vapor bubbles in the hydraulic oil.

Thrust plate

Aeration is a form of cavitation that occurs when outside air is drawn into the hydraulic

10

27. As the bubbles, bubbles, created by cavitation and aeration, are carried around to the pump outlet, the increase in pressure squeezes the bubbles. An implosion implosion occurs when the the pressure becomes too great and the bubbles collapse inward.

CAVITATION &

Thrust plate 27

28. When the air bubbles implode intense intense shock waves bombard the surface of the wear plates. The shock waves waves erode the plates’ plates’ surfaces on the high pressure side and trapping groove area. The sealing capability of the plate is reduced resulting in a loss of output flow. The presence of air can also reduce the volume of oil available to carry away heat that is produced by mechanical friction. friction. Vacuum conditions created in the pump rob oil from the bearing and thrust plate areas. The loss of oil in bearing bore upsets the loading which can result in premature bearing failure. Thrust p ates, re y ng on t e o to ma nta n t e r balance become unbalanced, resulting in a milling of the plate surface. Physical damage can also be seen on the gear housing bore in the form of a rough surface in the gear wipe area.


CAVITAT AVITA TI O N & AVI TAT ATI AERATION

Thrust late 28


CAVITATION DAMAGE - Inlet restriction

29. Read slide slide text. text.

• Clogged inlet strainer / breather • Inlet strainer too small • Inlet line too long • Inlet line bore too small • Excessive engine speed • Collapsed inlet hose • Suction head too great • Oil too viscous ( cold weather)

• Noise • Heat • Accelerated wear – thrust – thrust plates / housing

• Internal leaks • Reduced um efficiency • Erratic actuator performance • Failed pump

11

AERATION DAMAGE


- Air enters oil • Low oil level • Vortexing of oil above strainer - whirlpool • Loose inlet fittings • Worn pump shaft seal • • Foam suspended in oil due to sloshing in the reservoir

30

• Noise • Heat • Accelerated wear – thrust – thrust plates / housing

• Internal leaks • Erratic actuator erformance • Reduced pump efficiency • Failed pump


CAVITATED THRUST PLATE

31. This plate has been damaged by cavitation. As the gear gear teeth come around around to the discharge side of the pump (outlet) the oil is exposed to the outlet pressure collapsing the large air bubbles.

OUTLET

INLET

31


CAVITATED THRUST PLATE

32. A close up of the plate shows the severity of the pitting. pitting. The damage is heaviest heaviest in the root seal area where the clearance between the plate and the gear gear face is the tightest. This damage allows high pressure oil to escape down the gear journal into the bearing or bushing.

12

CAVITATED MOTOR THRUST PLATE

33. Motor cavitation cavitation occurs when the supply pump cannot produce enough flow to keep up with the speed of the motor. The motor then begins begins to act as a pump. pump. This M75 series motor plate has cavitation damage on both sides of the plate. plate. This condition occurs when a motor is cavitated in both directions of rotation. The damage to this plate is heaviest in the trapping groove areas because the cav tat on u es create on t e pump s e of the motor are carried to the outlet side and are mechanically imploded by the meshing of the gear teeth.

33

34. Again, a close up shows shows the severity of the damage.


CAVITATED MOTOR THRUST PLATE

35. A loss of lubrication lubrication in the pump can also cause rifling of the gears and thrust plates. Air in the system creates an come in harder over one gear than the other. The gears try to separate and walk towards opposite ends of the pump. The effect is a milling of the plates behind the idler gear at one end of the pump and the drive gear on the other end. The torque needed to drive the pump increases dramatically and the pump becomes heated. The removal of thrust plate material will contaminate the hydraulic system. Note: The problem described above has been largely eliminated in the P300 series bushing pumps because of the new thrust plate design. However, all pumps pumps with an integral r ve s a t nc u ng t e ser es are susceptible to rifling if an external force is applied to the drive shaft (push or pulling force). An example of of this is an interference interference

34


RIFLED GEAR & THRUST PLATE

13

RIFLED THRUST PLATE

36. Milling damage is evident at the center of this thrust thrust plate. Not as obvious is the cavitation erosion on the plate at three o’clock.

37. The milling has not erased the tell tale erosion damaged caused by the cavitation. When the damage has progressed to this point the entire hydraulic system should be flushed and the filters and strainers checked.

36


RIFLED THRUST PLATE

37


PRE PR ESSU RE D A M A GE REPEATED HEAVY

38. Pressure and hydraulic hydraulic shock are also also causes of pump pump failure. Pumps operating operating under a continuous heavy load, (high pressure), and extended duty cycle are susceptible to premature premature wear and failure. orce orcess gene genera rate te y t e pump pump out out et pres pressu sure re and gear area causes a deflection of the gears. This stresses the bearings or bushings that support the gear journals. The oil film needed to lubricate and cushion the pump elements becomes thinner and thinner with the increase in pressure until direct contact is made. loading fractures the hardened surfaces of the needle bearings, bearing race, and gear journals. These fractures, over time, lead to a breakdown of the surface material. material. Small pieces of material break away leaving a rough running surface. The rough surface can no longer support the film of oil needed to lubricate and cushion the pump components. The damage quickly accelerates until a catastrophic failure occurs spreading contaminant throughout the hydraulic system. The bushing pumps rely more heavily on the film of oil to support the loaded gear journal. Clearances between the journal and bushing sur ace are greater greater than than the c earance n the bearing pumps. This is necessary necessary to support the thicker oil film. film. When subjected to repeated heavy loads a breakdown of the oil film allows direct contact of the bushing and journal. The PTFE coating, that protects the bushing I.D., wears away and an increase in friction friction and heat occurs. occurs. The bushin bushin surface surface becomes rough and the oil film can no longer be supported. Under continued operation and friction becomes severe and the bushing may start spinning spinning in the bore. Again a catastrophic

14 39. Read slide slide text. text.

PRESSURE DAMAGE

• • • • •

Improper relief valve setting Relief valve malfunctioned Slow acting relief valve Absence of a relief valve downstream of the valve affecting the relief valve performance

• • • • • • •

Accelerated wear Cracked housings Excessive housing cut-out Reduced efficiency Internal leakage ear ng us ng a ure Thrust plates coined, warped or cracked • Broken drive / connecting shaft

39

40. Extended operation under high pressures has caused the spalling of the needle bearings in this bearing. Surface cracks have lead to a fracturing of the needle bearing material. material. An increase in system noise and heat could alert the operator to this type of problem.

©1998 Commercial Intertech Corp.

BEARING FAILURE

40

41. This slide shows shows the inner race of the the bearing and the damage caused by excessive loading.


BEARING FAILURE

15

42. As the bearing bearing wears the gear journal journal becomes damaged by the direct contact of the journal to the needle bearings.

BEARING FAILURE

42


PRESSURE DAMAGED GEAR HOUSING

43

43. The system pressure deflects the the gears into the low pressure pressure inlet side of the the pump. If the system pressure increases above the pressure rating of the pump, then the gears deflect too far and the gear housing cut-out becomes excessive. Internal slip increases and the pump becomes less efficient. The contaminant contaminant created by the the cut-out can foul relief valves and other system components. If the housing housing cut-out exceeds .005” (.007” for a bushing pump gear housing) the gear housing should be replaced.


PRESSURE DAMAGED

44. Hydraulic shock loads can cause an immediate component component failure in your hydraulic system. Sudden pressure spikes that exceed the housing at the port location and bolt hole areas of the casting. casting. A slow acting or malfunctioning malfunctioning relief valve can cause excessive pressure spikes in the system.

16 45. Commercial Intertech’s engineering engineering department sets maximum pressure limits for all pumps by calculating bearing loads and . v , size in the gear housing the weaker the casting. The larger port requires the removal of a greater percentage of casting material and a reduction in the safety factor. Continuous operating pressures above the pump rating can lead to cracked housings due to fatigue.

PRESSURE DAMAGED GEAR HOUSING

45

46. Thrust plates can also be damaged by excessive pressure. The above plate split through the middle due to excessive loads. The thrust plates used in the roller bearing product are most susceptible to damage between the two gear bores. bores. A small bleed hole, needed for balancing pressures in the bearing bores, is machined on the back side of the plate in this area. Couple this this with fact that the greatest pressure in the pump occurs at the center of the plate where where the gear teeth mesh. The oblong bores in the above plate are due to a bearing failure.


PRESSURE DAMAGED THRUST PLATE

46

47. Excessive pressures pressures can also cause coining damage damage to the thrust plate. This is a deformation of material on the low pressure . v pushes the plate into the gear housing with enough force to cause a bulging of material in the relieved edge of the plate. plate. The major O.D. O.D. is flattened.


HEAVILY COINED THRUST

COINING

17

PRESSURE DAMAGED DRIVE SHAFT

48


48. Hydraulic shock and excessive pressure pressure can also cause failures to the pump drive line. Many times the drive coupling or pump drive . v , drive shaft broke where the shaft diameter is the smallest. The drive shaft was not strong enough to withstand the torque load generated by the high pressure. Each section of a multiple pump or motor should be regarded as a single unit with correspon correspondin din delivery delivery and and power power input input requirements. Since the entire input horsepower required to drive the pump is fed through a common drive shaft, the power delivered to or from the unit is limited by the physical strength strength of the shaft. This limit limit is defined as a “PL” factor; “P” being the the maximum operating operating pressure and “L” the

. “ ” maximum operating pressure by the gear width. Each style or type of shaft has a unique “PL” rating. rating. Tables are provided in each of the pump/motor pump/motor product catalogs defining the the “PL” rating for each shaft type. If the “PL” factor exceeds the catalog rating of your shaft choice select a new shaft type with an adequate “PL” rating. PL= Pressure X Total Gear Width Torsional fatigue can also cause a shaft to fail, having a similar appearance to the above shaft. With torsional fatigue fatigue failure, however, the core of the shaft across the break has a smeared appearance caused by repeated forces and a gradual gradual wearing out of the the shaft. (A sudden break is characterized characterized by a rough granular shaft core.) core.) Torsion forces acting on the shaft in the same direction tend to cause a break at a 450 angle to the shaft axis.

PRESSURE DAMAGED CONNECTING SHAFT

49. The connecting shaft in in a tandem pump pump has the smallest diameter in the pump drive line, many times making it the weak link. In multiple units the “PL” must be calculated for the the first first connectin connectin shaft as well well as the drive shaft. When calculating calculating the “PL” for the connecting shafts, the drive gear is not included. The calculation is made from from the first connecting shaft back.

49

18 50. Drive line misalignment misalignment can cause the pump shaft to flex with each revolution, often resulting in a clean break at a 900 angle to the . areas where stresses are concentrated, such as, holes, grooves, grooves, and reduced diameters. A rough spot on the smooth shaft core is where the shaft finally severed. 51. Heat is generated in a hydraulic hydraulic system whenever oil dumps from an area of high pressure to low pressure without doing mechanical work. Oil blowing over a relief valve or flowing through piping, a valve, a clogged filter or strainer all are examples of sources of heat. Proper reservoir size can dissipate much of the heat generated in a . must be added to sufficiently cool the oil. Other factors, such as, contamination, cavitation/aeration, improper oil viscosity can add to the heating problems of a hydraulic system.

ROTATIONAL BENDING FATIGUE FAILURE

50


HEAT HEAT

Heat build-up causes the hydraulic oil to loose its viscos viscosity ity result resultin in in an an oil that that no lon lon er meets specification. specification. This greatly greatly reduces the lubricating effects of the oil on the close tolerance parts. The heated oil oxidizes, oxidizes, encouraging corrosion, leakage, and the development of of sludge. Sludge can clog clog filters and strainers compounding system problems. leading to cavitation and additional heating of t eo . The close running tolerances of the pump/motor pump/motor components makes them susceptible to heat damage. Add the fact that the thrust plates are being squeezed against the gear faces with hydraulic hydraulic pressure; pressure; a loss of lubrication between the two surfaces can

• THINS THE SYSTEM OIL - increasing friction • ACCELERATES THE BREAKDOWN OF THE OIL - causing sludge to form • CAN BE CAUSED BY WORN COMPONENTS • EVERY 18° 18°F F RISE IN IN OIL TEMPERA TEMPERATURE TURE - doubles the rate of corrosion on exposed surfaces 51


HEAT DAMAGE

friction. 52. Read slide slide text. text.

• • • • • • • •

Low oil level Cavitation / aeration / water Contamination Inlet restriction Relief valve Incorrect fluid Poor reservoir design Undersized fittings, hoses, components

• • • • •

Breakdown of oil Loss of lubricity Accelerated wear Reduced efficiency Leakage

• Internal seal destruction • Seizure

19

53. With the loss loss of lubrication lubrication the thrust plate becomes heated rapidly. rapidly. If the condition condition persists persists the plates will become so heated that lead in the alloy will be drawn out of the plate.

Lead

Motion Motion Gear

Gear

Thrust plate 53


54. As the lead comes to the surface the trailing gear tooth smears the lead over the surface of the plate. The plate will will become blackened blackened by the lead oxidation.

HEAT DAMAGE

Motion

Gear

Thrust plate 54


HEAT DAMAGED THRUST PLATE

55. The thrust plate plate in this slide slide has been subjected to extreme heat causing the lead to be drawn to the surface. A blackened surface and thermal cracks in the plate can result.

20 56. Excessive heat can cause a thrust plate mate materi rial al to beco become me brit brittl tlee and and crac crack. k.

HEAT DAMAGED THRUST

56

57. This P300 series thrust plate has has been damaged by extreme heat due to a loss of lubrication. The surface is is blackened


57

58. Temperatures of 400 degrees Fahrenheit will melt the glass filled nylon channel seal . the two piece channel seal and the buna pocket seal will be damaged at a much lower temperature.



HEAT DAMAGED THRUST

21

HEAT DAMAGED GEAR

59

59. With excessive heat the the ends of the gear teeth near the gear face become discolored. The high heat causes a bluing of the teeth. W thrust plate plate will start to weld together. The continued motion of the gear tears thrust plate material from the plates surface. The friction can generate enough heat that the pump could eventually seize up.



60

60. Welding between between the gear face and the the thrust plate has occurred resulting in a ripping of material from the plate surface.


Small amplitude vibration

Contaminant suspended in grease

Coupling

Drive spline

61. Fretting is a condition that that occurs between the drive shaft extension and the drive coupling. These parts are commonly commonly lubricated with a heavy grease. Fretting damage occurs when the grease picks up grit and the small amplitude vibration makes the contaminated grease act like like sandpaper. As the wear progresses the clearance between the parts becomes greater allowing more shaft coupling movement. The wear accelerates until there is not enough engagement to carry . the coupling will spin on the shaft stopping the revolution of the pump gears and thus pump flow. The coupling coupling and the pump pump gear set will have to be replaced.

22 62. This splined drive shaft has been worn by by fretting corrosion. corrosion. To prevent this damage damage the drive coupling should be cleaned regularly

FRETTED DRIVESHAFT

synthetic grease.

62

63. Commercial Intertech performs a break-in test on 100% of it’s factory built pumps. Any pump repaired and rebuilt should also be tested. This gives the the unit a proper proper break-in and insures that it is performing to specification. The unit should also also be inspected for external leaks leaks at this time. time. The recommended test/break-in procedure is described in all the Commercial Intertech pump service service manuals. Fact, 99% of all rebuild errors can be found at the test stand.


REBUILD ERRORS

63



POTENTIAL ASSEMBLY

• Improper bolt torque • Nicked lip seal • Pinched / fretted section seal • Improper installation of thrust plate • Pinched pocket / channel seal

• • • • •

Heat Extruded section seal External leak Internal leak Reduced efficiency

23 65. Pinched or fretted section seals seals can lead to external leaks. If the section seal is not properly installed the seal can be flattened . v leak path for oil to escape.

PINCHED & FRETTED SEALS

65

©1998 CommercialIntertech Intertech Corp. ©1998 Commercial Corp.

SYSTEM MAINTENANCE

66. Your approach to system maintenance maintenance will either give you a reliable, relatively trouble free system or a system that is a constant maintenance nightmare. The best advise we can offer is to meet or exceed the Original Equipment anu anu actu acture rerr’s reco recomm mmen en at ons ons on maintenance intervals, and follow his recommendations when replacing critical system components.

MAINTENANCE

The OEM has engineered and assembled a hydraulic system which has been thoroughly tested and proven to give the best . 66


67. These are critical system system components. components.

THE THE SYSTEM SYST SY STEM EM INCLUDES: • • • •

Hydraulic Oil Hoses/tubing Fittings Filters

• Hydraulic Pump • Directional Valve • Actuator – motor – cylinder

24 68. Careless substitution of any critical system component with a substandard replacement will lead to extended downtime and .

SUBSTITUTIONS

68



HYDRAULIC OIL

closely as possible • Unnecessary Unnecessary additives may be detrimental • Do not mix and match

69



WHEN REPLACING , Use products with the same: – Size – Material – Length – ress ressur ure e ra ra ng

as the original equipment

25 71. Using “after market” hydraulic components can be a dangerous proposition.

HYDRAULIC COMPONENTS After market substitutions may lack proper: • Tolerances • • • • •

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Testing Pressure rating Safety factor a er a Design


SUBSTITUTIONS SUBSTITUTIONS CAN DEAL YOU A LOSING HAND

72. SUBSTITUTES CAN COST YOU BIG:

• added downtime! • additional repairs !! • additional cost!!!

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PUM U M P / M O TO R REPL RE CEM M EN T REPLA PLA CE

73. Replacing a worn or failed pump/motor pump/motor without taking the proper precautions can lead to rapid failure failure of the new unit. The tight factory tolerances of a new unit make it more susceptible to the same conditions that caused the first unit unit to fail. Flushing the the hydraulic system, changing filters, and replacing used oil with new can insure proper component life. The relief valve and the governor should be reset prior to resuming . ALWAYS USE AN ACCURATE GAGE WHEN ADJUSTING THE RELIEF

26 74. Before installing a new or or rebuilt pump pump or motor, back off the main relief valve until the spring tension on the adjusting screw is relieved. v damage to the replacement unit in the event that the relief valve setting had been increased beyond the recommended operating pressure prior to removing the old unit.

RECOMMENDED START-UP FOR NEW OR REBUILT PUMP/ MOTOR • • • • •

Insure system cleanliness Back-off relief valve pressure and reset governor Fill unit with clean oil before connecting lines Connect the lines and mount unit Operate the unit at zero pressure for a minimum of two minutes minutes at at low speed • Gradually increase speed and pressure to normal operating conditions - approximately 5 minutes • Reset the main relief valve while the unit is operating at maximum operating speed

Before connecting any lines to the pump or motor, fill all ports with clean oil to provide initial lubrication. lubrication. This is particularly particularly important where the unit is located above the oil reservoir. During the break-in period, the unit should run free and not develop an excessive amount of heat. Commercial’s pump/valve pump/valve units should should be started up in the shift to to raise position. This will insure a good prime and prevent heat damage.

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, ’ manufacturers of hydraulic components for the mobile market, has brought you this training program on Failure Analysis. If you have any further questions on this subject or any of our hydraulic products, please contact your Commercial Intertech Sales Representative or your nearest Authorized Distributor.

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Gear Pumps & Motors Failure Analysis Guide

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